This project aims to elucidate the functional activities mediated by adenylyl cyclase with special emphasis on the regulation of enzyme activity by GTP binding proteins and other modulatory factors. The transduction of extracellular signals across the plasma membrane occurs in all eukaryotic and prokaryotic organisms. In many of these systems, extracellular ligands interact with integral membrane receptors to initiate the transmembrane signalling. On the intracellular side of the membrane, activated receptors catalyze the dissociation of GTP binding protein subunits which in turn activate intracellular effector proteins including adenylyl cyclase, cGMP phosphodiesterase, phospholipase C, and numerous ion channels. The adenylyl cyclase enzyme, responsible for the generation of cAMP, plays a central role in many signalling pathways. It is expressed at extremely high levels in the vertebrate brain and its activity is modulated by many neurotransmitters. Elucidation of the function of this important enzyme and its regulation by protein-protein interactions is fundamental to an understanding of cellular activity in the nervous system. Abnormal activity of adenylyl cyclase or proteins that modulate its function have profound effects on development and differentiation as well as in learning and memory. The adenylyl cyclase enzyme has been the subject of considerable biochemical study. The recent molecular cloning of one form of the enzyme from bovine brain suggests a complex integral membrane protein. Among the aims of this proposal are: (1) to use molecular cloning approaches to characterize the proteins which are responsible for adenylyl cyclase activity in mammalian brain. (2) study the expression of distinct forms of adenylyl cyclase in an organism that is amenable to genetic manipulation. This includes examination of available genetic mutants in the enzyme which lead to profound memory and learning defects. (3) develop and use a genetic selection system to identify the functional domains of the enzyme responsible for catalytic activity and interaction with modulatory proteins. The information gained from these studies should provide significant insight into the mechanism of regulation of intracellular second messengers and the effect of their modulation in normal and abnormal neural function.